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Questions about the function Assuming[], the $Assumptions system variable, and the Assumptions option of functions such as Simplify[] and Integrate[].
1
vote
Accepted
Denominator negative, numerator negative but sign of fraction not positive?
From the help
Unless expr is manifestly True, TrueQ[expr] effectively assumes that
expr is False.
So expressions that do not simplify to True will not necessarily return
true even if they ar …
3
votes
Accepted
How to check the assumptions attached to a given symbol?
The function Refine does what you want
Assuming[x ∈ Reals, Refine[Element[x, Reals]]]
(* True *)
Assuming[x > 0, Refine[Element[x, Reals]]]
(* True *)
5
votes
Assuming[a ∈ Reals, Conjugate[a]] fails to invoke assumptions
The function that you need to apply assumptions is Refine. I use it quite often, when I don't need or want more complete simplification.
Assuming[a ∈ Reals, Refine[Conjugate[a]]]
(* a *) …
1
vote
Solving for positive square root of an equation, using assumptions
How about
Map[Sqrt,
Solve[K == ((1/Sqrt[1 - betasq]) - 1)*m*c^2, betasq], {3}]
(* {{Sqrt[betasq] -> Sqrt[(K^2 + 2 c^2 K m)/(K + c^2 m)^2]}} *)
5
votes
Using assumptions, weird output
Assumptions are not applied automatically. A minimal way to apply them is to use Refine. …
3
votes
Simplifying square roots of squared reals
Mathematica doesn't agree that the second result is simpler. It judges complexity (in part) by LeafCount. The second expression has a slightly higher value.
LeafCount[Sqrt[b^2 + b^4]]
(* 11 *)
Lea …
3
votes
Specify range of variable in a equation
I think you would like to show the result in terms of 1-h rather than -(-1+h). To achieve this, I would do the following
expr = FullSimplify[Integrate[t1^2*E^((1 - h)*s0*t1), {t1, 0, T}]];
rule = h …
2
votes
Why Mathematica is not assuming real variable as real?
I don't know really know why FullSimplify doesn't work, but Refine does
Assuming[{a >= 0, d >= 0, b1 >= 0, b2 >= 0, c >= 0},
Refine[({{Re[mat1[[1]][[1]]],
Re[mat1[[1]][[2]]], -Im[mat1[[1]][[1] …
1
vote
Simplifying Min with assumptions
Interestingly, providing a slightly weaker assumption works
Simplify[Min[a1 R1/q1, a2 R2/q2], a1 R1/q1 <= a2 R2/q2]
(* (a1 R1)/q1 *)
Whereas
Simplify[Max[a1 R1/q1, a2 R2/q2], a1 R1/q1 <= a2 R …
0
votes
What is the fastest way to simplify $\sqrt{a^2}$ for $a>0$
In a complicated expression, with many repeated subexpressions, it can be useful to extract the parts and simplifying before substituting back in
Union[Cases[exp, __Power, ∞]]
(* {b^2, Sqrt[a b^2]} * …
1
vote
Integrating a piecewise function with symbolic pieces
Note that in Piecewise the conditions are evaluated sequentially. Bearing this in mind, we can avoid (at least in this case) introducing a dependency on the (assumed fixed) relationship between t1 an …
1
vote
Problem with particular simplification of complex function under assumptions
If you want to prove that something is constant, you can try differentiating it
Assuming[-1 < z < 1, FullSimplify[D[expr, z]]]
(* 0 *)
0
votes
Problem with particular simplification of complex function under assumptions
If you think you know the answer, it is often easy to ask Mathematica to verify your suspicion
FullSimplify[ForAll[z, -1 < z < 1, expr == 1]]
(* True *)
1
vote
Accepted
Solving the matrix with assumption?
All the assumptions made in the following are consequences of the matrix M being positive-definite Hermitian. …
2
votes
Accepted
Assuming x real, simplifying or refining Im[1/(x+i)] doesn't yield anything
Use ComplexExpand to simplify, assuming variables are real
ComplexExpand[Im[1/(x + I)]]
(* -(1/(1 + x^2)) *)